Akt/protein kinase B and glycogen synthase kinase-3β signaling pathway regulates cell migration through the NFAT1 transcription factor

The phosphoinositide 3-kinase (PI3K) pathway regulates a multitude of cellular processes. Deregulation of PI3K signaling is often observed in human cancers. A major effector of PI3K is Akt/protein kinase B (PKB). Recent studies have pointed to distinct roles of Akt/PKB isoforms in cancer cell signaling. Studies have shown that Akt1 (PKBα) can attenuate breast cancer cell motility, whereas Akt2 (PKBβ) enhances this phenotype. Here, we have evaluated the mechanism by which Akt1 blocks the migration of breast cancer cells through the transcription factor NFAT. A major effector of Akt/PKB is glycogen synthase kinase-3β (GSK-3β), also a NFAT kinase. Inhibition of GSK-3β using short hairpin RNA or a selective inhibitor potently blocks breast cancer cell migration concomitant with a reduction in NFATactivity. GSK-3β-mediated inhibition of NFATactivity is due to proteasomal degradation. Experiments using GSK-3β mutants, which are unresponsive to Akt/PKB, reveal that inhibition of cell migration by Akt/PKB is mediated by GSK-3β. These effects are recapitulated at the levels of NFATdegradation by the proteasome. Our studies show that activation of Akt/PKB leads to inactivation of the effector GSK-3β and the outcome of this signaling event is degradation of NFATby the proteasome and subsequent inhibition of cell migration. © American Association for Cancer Research.